1. Field of the Invention
This invention relates to rubber compositions suitable for use particularly as inner linings in automobile tires.
2. Description of the Prior Art
Halogenated butyl rubbers are known in common use as inner liners for automotive tires. These rubbers are acceleratively sulfur-vulcanizable with use of certain accelerating agents. Dibenzothiazyl disulfide (DM) has been proposed to this end as disclosed for instance in Japanese Patent Laid-Open Publication Nos. 57-172945, 57-195760 and 59-89208. Japanese Patent Laid-Open Publication No. 59-120501 is directed to incorporating tetramethylthiuram disulfide (TT). A still another accelerated system of sulfur vulcanization is that two different accelerators are combined as taught in Japanese Patent Publication No. 57-49405 which involves the use of TT/DM or alkylphenol disulfide (APDS)/DM. Japanese Patent Laid-Open Publication No. 55-80446 discloses that halogenated butyl rubbers may be used to improve durability of tire sidewalls.
DM would often make the resulting rubber composition readily susceptible to blooming and hence less tacky in an unvulcanized state, and therefore, hardly processable. Blooming is the more frequent the higher the processing temperature. TT would be ineffective for improving tack strength, whereas APDS would be less resistant to scorch usually taken to mean premature vulcanization. Moreover, TT and APDS would lead to excessive crosslinking, resulting in a vulcanizate of inadequate elongation.